Researchers have for the first time discovered evidence of green peach aphid (GPA) populations displaying sensitivity shifts to sulfoxaflor, the active ingredient in Transform™, pointing to the first signs of resistance evolving in Australia.
GPA is a widespread pest of canola and pulse crops and a key vector of turnip yellows virus (TuYV), which severely affected crops in parts of south-eastern Australia in 2014.
Sulfoxaflor, a group 4C insecticide, is an important tool in GPA management in canola, particularly since effective chemistries are limited.
In Australia, GPA is known to have developed resistance to synthetic pyrethroid, carbamate, organophosphate and neonicotinoid insecticides.
Resistance to dosages below the field rate of sulfoxaflor has recently been detected in a small number of GPA populations collected near Esperance, in Western Australia.
The discovery was made through collaborative research by cesar, CSIRO and the WA Department of Primary Industries and Regional Development (DPIRD).
The research was the result of a co-investment by GRDC and Corteva Agriscience™.
The low-level resistance has been shown to persist after multiple generations of culturing in the laboratory, demonstrating there is an underlying genetic basis.
In parts of Europe, GPA has developed high levels of resistance to neonicotinoids, due to a mutation known as R81T, which also confers cross-resistance to sulfoxaflor, albeit at a reduced level.
Importantly, Australian populations of GPA have tested negative to this genetic mutation, including those collected near Esperance.
While Transform™ remains a highly effective means to control GPA, this discovery serves as an important reminder to use the product judiciously.
For species such as GPA, which has a high propensity to evolve new resistance, this means only spraying insecticides when absolutely needed.
There are unlikely to be yield losses from TuYV infections after the rosette stage in canola.
The risk of direct feeding damage from GPA is also low in later-stage canola crops. Although, in seasons such as 2018, aphids can build up to high population levels and inflict serious damage, particularly when plants are moisture-stressed.
When insecticide applications are warranted, a key resistance management strategy is to rotate chemical mode of action groups. Although, growers are limited in this approach due to the existence of resistance to other registered foliar insecticides across Australia.
It is therefore important to take an integrated approach to GPA management.
When insecticide applications are warranted, a key resistance management strategy is to rotate chemical mode of action groups.
Green bridge control and deterring aphid landings during autumn by sowing into standing stubble are two tactics that growers can use to reduce reliance on insecticides.
Conserving beneficial insects, such as ladybird beetles, lacewings, hoverflies and wasps, early in the season with the use of soft chemistry, is critical to IPM.
When using Transform™ to control GPA, it is essential that the product is applied with optimum coverage. Transform™ exhibits only acropetal movement in the plant (it moves upwards in the xylem or stem) and does not translocate downwards.
In order to control GPA populations colonising older canola leaves, applications should be made before crop canopy closure and by using appropriate spray technologies.
It is critical that spray booms are set up to deliver the chemical where the aphids are located. High water volumes, correct nozzle selection and appropriate ground speeds help to ensure that Transform™ gives the expected efficacy.
It is also critical that the full label rate for Transform™ is used, as lower rates will often prove to be ineffectual and only serve to increase selection pressure for further resistance.
For canola, the label rate of Transform™ WG is 50 grams per hectare.
GRDC has a range of information about recommended water volumes, nozzle selection and appropriate ground speeds.
Currently, the populations of GPA demonstrating low-level resistance are confined to the Esperance region.
In order to limit the spread and restrict the further evolution of resistance, it is vital that Transform™ is used responsibly within the framework of an Insecticide Resistance Management Strategy (IRMS). Following label directions and ensuring excellent coverage are critical to ensure best results.
Growers are encouraged to follow recommendations outlined in the GPA IRMS, which was developed by the National Insecticide Resistance Management working group. Although some updates to this strategy are needed, it remains the best source of information for growers.
Growers are urged to keep a close eye on establishing canola crops this year and to contact their state agriculture department or cesar - on 03 9349 4723 - if aphids survive a Transform™ application.
More information: Dr Paul Umina, firstname.lastname@example.org
Acknowledgements: Dr Rob Annetts, Corteva Agriscience™.